There is no denying that Sonos has made streaming audio both convenient and simple for today's home. We have had Sonos in our home since its initial release and it continues to be the best and most used product by members of the household. While Sonos generally sounds great, audiophiles may find there is room for improvement when it comes to the DAC and amplifier used in the original ZP100 and the more recent CONNECT:AMP (formerly the ZP120) Zone Players. Unfortunately, the built-in amplifiers in the CONNECT:AMP are limited in both power and low impedance drive capability.

The Solution
AudioControl has addressed this need with the release of the Rialto 400 ($799), which features a great sounding Wolfson® DAC (WM8761) along with an integrated high power two-channel amplifier to satisfy audiophiles wanting more from the current Sonos products. The DACs used in the Wolfson WM8761 are implemented using sigma-delta over-sampled conversion techniques. This requires that the PCM samples are digitally filtered and interpolated to generate samples at a much higher rate than the (up to 192kHz) input rate. The sample stream is then digitally (sigma-delta) modulated to generate a digital pulse stream that is then converted to the analog domain in a switched capacitor DAC. The advantage of this topology is that the DAC is linearized using noise shaping techniques, allowing the 24-bit resolution to be met using non-critical analogue components. In addition, the high sample rate at the DAC output minimizes the slope of the smoothing filters on the output of the DAC. The multi-bit switched capacitor technique used in the DAC reduces sensitivity to clock jitter, and dramatically reduces out of band noise compared to switched current or single bit techniques used in many other designs.

The Rialto 400 provides an impressive 100 watts per channel into 8 ohms and 200 watts into 4 ohms, which says a lot about the current drive capability of the amplifier design. The unit gets significantly warm when operating, so we would recommend that users provide adequate ventilation when placing the Rialto 400 in their system. The Rialto 400 is stated to have an SNR (Signal-to-Noise Ratio) >95dB and a THD (Total Harmonic Distortion) of 0.09%. There is a 3.5mm headphone jack on the front for convenience, which automatically mutes the speaker outputs when being used.

The Rialto 400 weighs just under 5 pounds and measures 8.6” (W), 2.9” (H), and 5.4” (D), with more depth needed for the banana jacks on the back. This unit is smaller than the Sonos ZP100 we have on hand and pairs nicely with the non-amplified Sonos ZP80.

Protection Features
The Rialto 400 amplifier has protection features that prevent damage from occurring. Normally the front indicator is dim red (standby) or blue (active source detected). The indicator will turn bright red if the unit has gone into protection mode or flash red when an over-current condition has occurred.

Rear Panel
The Rialto 400 is designed to accept a wide range of audio sources including digital (via coaxial and toslink), line level analog (via RCA and 3.5mm), and even direct speaker output connections from a receiver. There are four analog style level controls for digital, analog, and speaker inputs as well as an AccuBASS level allowing users to adjust the right settings for their configuration. A sub/mono output offers additional flexibility should the user want to add a mono channel or powered subwoofer. The IEC power jack accepts both 120/240 type cables with a switch to select the appropriate voltage range. The 12 volt trigger input provides custom installers with the ability to turn the unit on and off from another controller. Finally, the five way binding posts allow for flexibility when connecting your speakers.

AudioControl’s SMART Signal Sensing lets the user prioritize which input to use based on personal preference. Input priority is set using the DIP switches allowing digital or analog priority to be set. The switches are also used to enable/disable the Standby mode. The default configuration automatically searches for the preferred active signal and decodes the appropriate source with one of the system's digital or analog inputs.

Stereo/Mono Switch
Underneath the Rialto 400 there are two switches. The Stereo/Mono switch configures the unit for standard stereo (two channel) operation or mono providing up to 400 watts (8 ohms) in the bridged mono mode.

Grounding Switch
The Grounding
switch selects
the
level
of
isolation
between
the
audio
signal
return
and
earth
ground.
Normally, this
switch
is configured in
the
‘ground’
position unless
AC
hum (often caused by ground loops) becomes an issue. Two alternate settings (R/C and Float) can be used to help remedy hum issues. Regardless of the switch setting, the
chassis
is
always
connected
to
the
earth
ground
for safety reasons.

Performance
We connected the Rialto 400 to our M&K S150-THX speakers to see what this unit was capable of delivering. The M&K speakers are nominally rated at 4 ohms and are not that efficient. However, these speakers sound great and we are used to their sonic character. Using the Sonos ZP80 as a digital source, we connected the optical cable provided with the Rialto 400. While I was tempted to keep the digital level adjustment on the back at full tilt, it was better set at a slightly lower level to minimize the low level noise in the background audio. Even at a lower level setting there was plenty of headroom allowing for high volume playback. Having independent control of each of the inputs allows for precise level matching, so that audio plays at the same level regardless of the source that is selected.

AccuBASS™
AudioControl's AccuBASS™ circuitry worked well and provided a much more enthusiastic bass response to many audio tracks we listened to. The variable level control allows users to dial in just the right amount of bass boost needed to enrich the listening experience. It is a great addition to a great sounding and powerful DAC/amplifier offering high resolution playback with the power and authority of a higher-end system. The compact design of the Rialto 400 allows it to be integrated into virtually any environment without taking up much space.

Thermal Considerations
The Rialto 400 generates a substantial amount of heat reaching temperatures as high as 115 °F (46 °C) on the top of the unit in an open environment. If installers plan to place the Rialto 400 in a cabinet, special thermal considerations may need to be addressed to ensure long-term reliability of the unit.

Conclusion
AudioControl has filled a real need with the introduction of the Rialto 400 and now audiophiles now have a great high performance alternative to the existing Sonos products, which have been more focused on convenience and not necessarily on high-end audio quality. The integrated Wolfson® WM8761 DAC coupled with the high performance two-channel amplifier in the Rialto 400 make it a great addition not only to Sonos systems, but to many other installations where high quality audio is desired from digital and analog sources. The additional features for selectable input priority and the inclusion of AudioControl's AccuBASS™ make the Rialto 400 a very attractive product for custom installers as well. AudioControl offers a 5-year limited warranty on the Rialto 400.